A vacuum vapor deposition method and a wet film formation method are methods used to form organic layers of an organic electroluminescent element. For its ability to easily achieve lamination, the vacuum vapor deposition method is advantageous in terms of improving charge injection from an anode and/or a cathode, and easily trapping excitons in the light-emitting layer. On the other hand, the wet film formation method does not require the vacuum process, and can easily achieve large areas. Another advantage is that the wet film formation method, with the use of a coating liquid prepared by mixing a plurality of materials having various different functions, can easily form a layer containing different materials with different functions. However, because lamination is difficult to achieve with the wet film formation method, the wet film formation method is inferior in terms of drive stability compared to elements formed by the vacuum vapor deposition method, and, with a few exceptions, has not reached a practical level.
In order to achieve lamination by the wet film formation method, there accordingly is a need for a charge-transporting polymer having a crosslinkable group that becomes insolubilized after being coated. There is an ongoing development of such charge-transporting polymers. Specifically, PTL 1 to PTL 4 disclose polymers in which benzocyclobutene, which provides desirable durability, is contained as a crosslinkable group, and an arylamine structure, which provides desirable transporting ability, is contained as a charge-transporting moiety.